(A) Field of the Invention
This invention relates to an improved coated abrasive belt, and more particularly, to an improved sectional coated abrasive belt having a width in excess of fifty inches.
(B) History of the Prior Art
In recent years, many applications have been developed that require the use of coated abrasive belts that have widths in excess of about 50 inches. The manufacture of such wide belts poses a serious problem to the coated abrasive industry. Commonly available equipment is not capable of coating backings that are wider than about 50 inches, and the cost of equipment that would be required to coat wider backings is prohibitive.
Many proposals have been made in the past to manufacture wide belts by splicing together sections of abrasive coated backing material. To make a belt that will operate smoothly, the joints between the sections must be at an angle to the direction of belt travel. To make the joint, the layer of abrasive is usually removed, and in some cases the abrasive is ground off both the bottom and top laps of two sections that are to be joined. Adhesive is then applied to the ends where the segments are to be joined, and the two ends are brought together in alignment between the platens of a press. The adhesive is then cured commonly under pressure.
In making such joints, it is difficult to obtain perfect alignment of the laps, and it is not unusual to obtain a joint that has a greater thickness than the abrasive coated backing, so that the belt has a tendency to bump in use. This produces undesirable finishing and grinding results, and accelerates belt wear on and in the vicinity of the splice area.
To minimize the effects of variations in belt thickness, it is common to dispose the joints at an angle to the running direction of the belt. One common technique for making wide, sectional belts involves cutting a coated abrasive web into a series of parallelograms, and joining these parallelograms along their longer sides. The belt that is thus obtained has the warp threads of the sections disposed at an angle to the running direction of the belt. Usually this angle is in excess of 45.degree., so that the strength and stretch of the belt are determined in large part by the cross tensile strength and cross stretch, respectively, of the backing of which the sections are made. In most cases, when standard finished drills or jeans cloth is used, these characteristics fall considerably short of what industry desires and needs. It is understood that warp filaments are those which run lengthwise in the loom or other clothmaking apparatus. Weft or fill filaments are those which run crosswise in the loom. "Filaments" as used herein is intended to cover threads, yarn, monofilament fibers or combinations of such fibers. Such filaments may be natural or synthetic. trapezoidal, abrasive coated segments together so that their warp threads always extend in the running direction of the belt. While this produces a belt whose tensile strength and stretch characteristics are more susceptible of control, there are many places along the length of the belt where three segments come together in a joint, and it is very difficult to form these joints with the same thickness as the remainder of the belt. Furthermore, because of the larger number of segments that must be joined together to make such a belt, labor costs are quite high.
To minimize conditions making for stretch in the cross direction, essentially the running direction in a sectional belt, it has been proposed to provide a backing member of sateen construction and to employ a minimum of tension in the warp direction during cloth finishing, see e.g. U.S. Pat. No. 3,053,020. Moreover, in a preferred proposal a sateen weave cloth backing member is selected and finished so that it is characterized by having practically equivalent strength and stretch in both the warp and fill (cross) directions. A finishing method to reduce stretch and improve strength in the running direction is also disclosed in U.S. Pat. No. 3,787,273. Nevertheless, while such fabric constructions and finishing conditions have resulted in some improvement in sectional abrasive belts, the search has continued for even further improvement in the stretch characteristics of such wide belts.